Ambient Light Sensors
General Application Note
Abstract
This application note introduces ambient
light sensing on a general level. The
different types of ambient light sensors are
described
and
related
to
specific
applications.
•
Automatic dimming of instruments in
automobiles to ensure reliable visibility
under all circumstances.
Automatic dimming of lamps for office
buildings, exterior lightings and traffic
signals.
Headlamp control in cars improves road
safety by automatically turning on the
lights in twilight or when entering a
tunnel.
•
Introduction
OSRAM OS offers a variety of ambient light
sensors. This application note introduces the
basic facts of ambient light sensing and
describes the characteristics of various
ambient light sensors. Detailed application
notes for specific sensor types are available.
•
Basic facts about ambient light
sensing
Brightness
Brightness is a term that describes how
intense a light source is perceived by the
human eye. Brightness is measured in units
called “LUX”. Light sources with the same
LUX level appear at the same brightness to
the human eye. Table 1 shows the bright-
ness (LUX measurement) of some everyday
light sources. The technical term for
brightness is illuminance.
Light source
candle (1m distance)
street light
office desk lighting
overcast day
overcast sunny day
direct sunlight
brightness
[Lux]
1
20
750
3000
20 000
100 000
Applications for ambient light
sensors
Ambient light sensors are photo detectors
which are designed to perceive brightness in
the same way as human eyes do. They are
used wherever the settings of a system have
to be adjusted to the ambient light conditions
as perceived by humans. The below list
describes typical applications for ambient
light sensors:
•
Saving battery power.
Ambient light sensors provide power
saving solutions for hand-held electronic
devices such as PDAs, mobile phones
and notebook PCs. Nearly all LCD
displays and keypads have backlighting.
Studies have shown that backlighting is
only required about 40% of the time. An
automatic adjustment (auto dimming) of
the backlight offers considerable power
savings.
Automatic dimming of flat panel displays
such as LCD screens to maintain the
same display appearance under all
lighting conditions from darkness to
bright sunlight.
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Table 1: Lux measurement of every day
light sources.
Spectral sensitivity
Spectral sensitivity relates to where on the
light spectrum a sensor is most effective.
•
29.06.2006
OSRAM [ OSRAM GMBH ]
